These types of crowns comprising a disconnecting gear device are known in the prior art. Such devices are known to be implemented, for example, to prevent damaging the mechanism of a timepiece when the winding stem is driven by the user to wind the barrel spring, when the latter is completely wound.
U.S. Pat. No. 2,637,987 discloses several embodiments of a crown of the aforementioned type. In all of the embodiments disclosed, the crown comprises a cylindrical housing inside which the disconnecting gear device is arranged. In particular, the housing comprises, at the periphery thereof, a strip spring secured to the crown, for cooperating with one end of the winding stem arranged inside the housing. For this purpose, the end of the winding stem has a particular shape, peculiar to each of the embodiments disclosed, fitted to the shape of the corresponding strip spring.
The cooperation between the strip spring and the winding stem is effective as long as the rotational couple to be transmitted to the winding stem from a rotation of the crown, via the strip spring, does not exceed a predefined value. When this predefined value is attained, which may be the case for example when the barrel spring is completely wound, the strip spring is deformed and stops cooperating with the winding stem. Thus, any subsequent rotational movement of the crown in these conditions is no longer transmitted to the winding stem.
The device disclosed in this American Patent has, however, a certain number of drawbacks. In fact, the structure disclosed and shown is complex both from the manufacturing and assembly point of view, in particular because of the dimensions to be considered within the field of crowns for horology. Manufacturing the various springs implemented is difficult, on the one hand because of their shape, and on the other hand, because they are mounted pre-stressed, which makes it difficult to mount them in the crown.
Another drawback of the device disclosed in U.S. Pat. No. 2,637,987 arises from the necessity of providing a particular shape for the end of the winding stem arranged inside the crown, such that it can cooperate with the particular shape used for the spring. This constraint forces the manufacturer to provide different manufacturing processes for the different winding stem shapes to be used, thereby causing extra costs.